Sugar beet thinner



ti ned States Patent Waldo 1. Weeks [72] Inventor Caldwell, Idaho '[21] App'LNo. 563.777 [22 Filed ,Iuly8,'l966 [45] Patented Oct. 13,1970 [731 Assignee by direct and mesne assignments to International Electric Fence Company, Inc., Albert Leo, Minn., a corporation of Washington [54] SUGARBEETTHINNER 8 Claims, 9 Drawing Figs.

[52] U. S.Cl.' 172/6. 47/143 [51] lnt.Cl ..A01b4l/06 [50] FieldofSearch 172/5,6, 48,108;47/1.43

[56] References Cited UNITED STATES PATENTS 492,867 2/1893 Hyde 172/48 3,027,950 4/1962 Cascarinc... l72/108X 3,308,890 3/1967 Rhode 172/6 Primary Examiner-Edgar S. Burr Attorney Hill, Sherman, Meroni Gross and Simpson ABSTRACT: A plant thinner including ground engaging wheels which are coupled to a distance measuring switch circuit and which has a cutter assembly comprising a pair of op posed blades that swing transversely to movement of the thinner and wherein the ends of the blades are spaced apart to allow plants to pass when the blade is moved. A magnetic clutch connects the cutter assembly to the ground wheels and photosensitive switch means detect the presence of plants beneath the machine and the distance measuring switch and the photosensitive switch are connected in circuit with the magnetic clutch to actuate the cutter assembly under selectable conditions.

M6 I r i so Patented Oct. 13, 1970 I Sheet of 5 I N V EN TOR.

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Sheet INVENTOR.

Patented Oct. 13, 1970 3,533,474

Sheet 3 015 JNVENTOR; W44 00 WEEKS, BY

I 504x440, 525M 41 Patented Oct. 13,1970

Sheet WUUSQ -BY jhwmdv iwww/ 4rroe/veys.

SUGARBEET THINNER This invention relates to agricultural machines, and more particularly to a crop row thinning attachment adapted to be mounted on a tractor and being especially useful for controlling the thinning of plants, such as sugar beets, and similar crops. v f A main object of the-invention is to provide a novel and improved row crop thinning apparatus adapted to be mounted on the cultivator bar of a tractor or on any other convenient part of a tractor or similar vehicle, the apparatus being simple in construction, being easy to instalL'involving relatively few parts, and employing photoelectric means for automatically thinning out a row of plants so as to leave a desired predetermined spacing therebetween.

A further object of the invention is to provide an improved crop thinning attachment for a tractor, which is especially useful for thinning out row crops, such as beets, or the like, the attachment involving relatively inexpensive components, being automatic in operation, and being provided with safety means to assure proper operation thereof.

A still further object of the invention is to provide an improved plant thinning attachment for a tractor, the attachment being provided with means for thinning out plants to provide a desired spacing therebetween, said means being adjustable so that the desired spacing may be set to a precise value, the apparatus being relatively compact in size and light in weight so that it can be easily installed and so that it does not interfere with the movement of the tractor with which it is associated.

A still further object of the invention is to provide an improved plant thinning attachment for use with a tractor, said attachment employing photosensitive means in conjunction with a suitable light source to respond to the presence of the individual plants in a row of plants to be thinned, the attachment involving relatively inexpensive components, being reliable in operation, being easy to maintain in operating condition, and being provided with plant spacing adjustment .means which is very easy to operate.

attachment constructed in accordance with the present invention, shown associated with a wheeled frame adapted to be attached to a tractor or similar vehicle.

FIG. 2 is a side elevational view of the plant thinning attachment of FIG. 1, taken from the opposite side.

FIG. 3 is a top plan view of the plant thinning attachment of FIGS. 1 and 2.

FIG. 4 is an enlarged cross-sectional view taken substantially on the line 4-4 of FIG. 3.

FIG. 5 is a transverse vertical cross-sectional view taken substantially on the line 5-5 of FIG. 4.

FIG. 6 is an elevational detail view taken substantially on the line 6-6 of FIG. 3 and illustrating the opposite positions of swinging movement of the thinning blade assembly of the apparatus. I

FIG. 7 is a fragmentary longitudinal vertical cross-sectional view taken substantially on the line 7-7 of FIG. 3.

FIG. 8 is a transverse vertical cross-sectional view taken substantially ontheline 8-8 of FIG. 7.

FIG. 9 is a circuit diagram showing the electrical connections of the various electrical elements employed in the thinning machine of FIGS. 1 to 8.

Referring to.the drawings, 11 generally designates an improved plant thinning attachment constructed in accordance with the present invention. The attachment 11 comprises a generally horizontally-extending main frame 12 which .may

. comprise a longitudinally-extending downwardly facing elongated box-like member provided with forward and rear pairs of depending arms 13,13 and 14,14, said arms being integrally formed with and depending from the respective depending side flanges 15,15 of the downwardly facing box-like frame member 12. Journaled between the lower portions of the pairs of depending arms are respective ground-engaging supporting wheels 16 and 17, said wheels having respective axles 18 and 19' suitably journaled in the respective pairs of arms 13,13 and 14,14.

Designated at 18 is a transverse shaft which is journaled on the rear portion of the frame member'l2, being rotatably supported, for example, on an upstanding bearing block 19 rigidly secured to frame member 12 at its rear portion and provided with a ball bearing assembly 20 in which the intermediate portion of shaft 18 is rotatably supported. Mounted on the frame member 12 is a conventional magnetic clutch assembly 21 provided with a magnetic clutch disc member 22 through which the shaft 18 extends and to which said shaft is centrally secured, as by a suitable key 23. The disc 22 represents the driven element of the magnetic clutch assembly 21. The driving element of the magnetic clutch is shown at,24 and is rigid with a sleeve 25 which is rotatable around and which receives the shaft 18, said sleeve being rigidly connected to a driving sprocket wheel 26. Sprocket wheel 26 is drivingly coupled by a sprocket chain 27 to respective driving sprocket wheels 28 and 29 secured on the shafts l8 and 19 of respective groundengaging wheels 16 and 17. Thus, the driving member 24 of the magnetic clutch assembly 21 rotates responsive to the forward movement of the frame 12.

Pivotally connected to the forward portion of frame 12 is a yoke member 30 whose side arms are pivotally connected to the depending side flanges 15,15 of the frame member 12 by suitable transverse bolt means 31', comprising a bolt extending transversely through the flanges 15,15 and provided at its outer end with a retaining nut 32, whereby the yoke member 30 may pivoton a transverse axis. The bight portion of yoke member 30 is provided with at least one pair of upstanding connecting lugs 33,33 for connecting the attachment to a suitable drawbar member 34, which, in turn, may be connected to the tool bar of an associated tractor or other hauling vehicle,

As will be apparent from FIG. 2, when the frame 12 is pulled by its associated hauling vehicle, the ground-engaging wheels 16 and 17 rotate-and transmit torque to the sprocket wheel 26 by means of the chain 27, causing said sprocket wheel and the clutch driving element 24 to rotate.

When the operating coil 35 of the clutch assembly 21 is energized, member 24 is drivingly engaged with disc member 22, whereby sprocket wheel 26 is coupled to shaft 18, causing shaft 18 to rotate.

Rigidly secured to the end portion of shaft 18 opposite sprocket wheel 26 is a wobble disc" 36 whose plane is inclined at a substantial angle with respect to a plane perpendicular to shaft 18, as is clearly shown in FIG. 8. An outer race ring 37 surrounds the wobble disc 36 and is substantially coplanar therewith, being retained in coplanar relationship therewith by the provision of suitable ball bearings between the inside periphery of the ring 37 and the peripheral edge of the disc 36, the ball bearings being retained in suitable peripheral grooves provided in the opposing surfaces of the members 37 and 36. Thus, rotation of the wobble disc" 36 causes the ring 37 to oscillate.

A yoke member 38 is pivotally connected to diametrically opposite portions of the ring 37 at 39,39, the yoke member 38 being secured to a downwardly and forwardly-inclined shaft 40 located laterally adjacent to and in a plane substantially parallel to one side of the frame member 12, the lower portion of the shaft 40 being suitably journaled in a bearing assembly 41 secured to the adjacent side flange 15 of the frame member 12, as shown in F IG. 1. Thus, the oscillation of ring 37 caused by rotation of shaft 18 is transmitted to the yoke 38, which causes shaft 40 to oscillate on its axis, following the motion of the pivot axis defined by the pivotal connections 39,39 of yoke 38 to ring 37.

Designated at 42 is a clamping sleeve assembly which is rigidly secured to the lower end of shaft 40 and which is arranged in a substantially vertical transverse plane, the clamping sleeve assembly 42 being provided with a squared receiving passage in which is engaged a squared bar 43, the bar 43 being clamped in adjusted position in the'sleeve assembly 42. Thus, the sleeve assembly 42 may include a clamping plate 44 which is forced against one side of the bar 43 responsive to the tightening of the sleeve clamping bolts 45, whereby the bar 43 is locked in adjusted position in the bar-receiving groove 46 of the main body portion 47 ofthe sleeve assembly 42.

Rigidly secured to opposite sides of the lower portion of the squared bar 43 are opposing, generally C-shaped hoe blades 48,48, said hoe blades terminating in downwardly and inwardly-inclined sharpened edge portions 49,49. The downwardly and inwardly-inclined blade portions 49 are arranged so as to be substantially horizontal at the opposite ends of the swinging movements of the arm 43 produced by the oscillation of shaft 40, as shown. for example, in FIG. 6. The arm 43 is adjusted so that the blade portions 49 will be somewhat below ground level when in their aforesaid horizontal positions. namely, will be at the proper depth to remove plants to be thinned as the machine 11 is pulled forwardly along a row of such plants. The sharpened ends of the blade portions 49 are adapted to penetrate into the soil, the blade portions being relatively thin so that they can be pulled through the soil easily and so that they can function as cutting means to sever and disengage young plants from the soil. The ends of the blade members 49 are spaced apart sufficiently so that in the intermediate position of the oscillation or swing of shaft 40, sufficient clearance is provided between the opposing ends of the blade elements 49 to allow the machine 11 to be pulled forwardly without engagement of the blades with any plants in the row.

As will be presently described, the thinning action is controlled automatically in response to the presence of plants 50 in the row to be thinned. The apparatus is triggered by photosensitive means, comprising a photoelectric relay assembly 51 suitably mounted on the side flange l forwardly adjacent the thinning blade assembly with its photocell 52 (see FIG. 9) suitably oriented to receive light rays from plants 50 there beneath, the plants beneath the photoelectric relay SI being illuminated by light from a suitable light source 53 attached to the adjacent depending arm 13 and directed downwardly, as shown in FIG. 1, so as to illuminate plants under the downwardly facing photocell 52 of the photoelectric relay assembly 51.

As shown in FIG. 9, the photoelectric relay assembly 51 is generally of conventional construction and includes a suitable amplifier 54 and a relay 55 controlled by the photocell 52 through said amplifier. Relay 55 is normally deenergized so that its armature 56 is disengaged from its associated stationary contact 57. The photocell 52 responds to the presence ofa plant therebeneath to cause relay 55 to become energized and close its contacts 56,57.

When the clutch coil 35 is energized, the forward movement of the machine 11 causes the shaft 18 to be rotated in a clockwise direction, as viewed in FIG. 7. Clockwise rotation of shaft 18 is normally limited by the provision of a stop cam 58 rigidly secured on shaft 18, the cam 58 comprising a pair of semicircular lobes 59,59 which are offset along a diametral line, thereby defining diametrically-opposed stop shoulders 60,60 where the cam radii suddenly changes in size. The shoulders 60 are alternately engageable against the top end of a pivoted locking arm 62, the arm 62 being pivotally mounted on the frame member 12 at 63 for swinging movement in the plane of the stop cam 58. Arm 62 is biased in a counterclockwise direction, as viewed in FIG. 7, namely, toward locking position, by a coil spring 64 connecting the arm 62 to an anchor ring 65, on frame 12, the anchor ring 65 being located leftward of thepivotal connector 63, as viewed in FIG. 7, to bias arm 62 toward locking position with respect to the stop shoulder 60. A release solenoid 66 is mounted on frame member 12 in a position to the right of arm 62, as viewed in FIG. 7, the plunger 67 of said solenoid being pivotally connected at 68 to a lug provided on the intermediate portion of arm 62. When solenoid 66 is energized, the plunger 67 rotates arm 62 in a clockwise direction against the tension of the spring 64, moving arm 62 out of locking position and releasing cam 58 and shaft I8 for rotation.

Mounted on diametrically opposite portions of the cam 58 are respective limit switch operating abutment members 69, 70 which are respectively engageable with the operating levers 71 and 72 of limit switches 73 and 74 mounted on the frame member 12 substantially at diametrically opposite locations with respect to the stop cam 58. As shown in FIG. 7, abutment member 70 engages the contact roller of arm 72 when the latch arm 62 underlies the adjacent shoulder 60, holding the switch 74 closed. When cam 58 is released, by the energization of latching solenoid 66, and cam 58 rotates in a clockwise direction, the switch 74 will open after a short preliminary period of rotation of cam 58, namely, after the abutment member 70 moves clear of the contact roller of the switch operating arm 72. The switch 73 is similarly released by the disengagement of abutment member 69 from the contact roller of the operating arm 71 of switch 73, but this occurs a short time before switch 74 is allowed to open. as will be presently explained. The abutment elements 69 and 70 are adjustably mounted on the cam 58 so that they can be set to provide the proper timing sequence of release of the switch operating arms 71 and 72.

As shown in FIG. 9. the switch assembly 73 comprises two switch poles 75 and 76 which are ganged together for simultaneous operation, the switch pole 76 normally engaging its associated stationary contact 77 (when abutment element 69 engages the roller of operating arm 71, as in FIG. 7) and the switch arm 75 being normally disengaged from its associated contact 78. When the switch operating arm 71 is released by the movement of the abutment member 69 clockwise sufficiently to releaseoperating arm 71, pole 76 disengages from contact 77 and pole 75 engages with contact 78. Thus, rota tion of cam 58 in a clockwise direction from the position shown in FIG. 7 first causes contacts 76,77 to open and contacts 75,78 to close, and after a short delay, allows the contacts of switch 74, shown at 79 and 80, to open.

The machine 11 includes a measuring device, designated generally at 81, for establishing a predetermined definite distance between thinned plants. Thus, the measuring device 81 comprises a housing 82 mounted on the frame member 12. Transversely joumaled in the sidewalls of the housing 82 is a shaft 83 on one end of which is secured a sprocket 84. The sprocket 84 is coupled by a sprocket chain 85 to a sprocket 86 secured on the end of axle 18', as shown in FIG. 1. Thus, the rotation of the ground-engaging wheel 16 drives shaft 83.

Rigidly secured on shaft 83 is a clutch disc element 87 which is part of a conventional magnetic clutch assembly 88. The assembly 88 includes the magnetic operating coil 89, the clutch disc assembly 87, and a cooperating clutch disc member 90 rotatably mounted on shaft 83 and being coupled to disc 87 responsive to the energization of the clutch operating coil 89. An abutment lug 91 projects from the marginal portion of disc 90, said lug 91 being biased into engagement with a stop arm 92 secured to one sidewall of housing 82 by a coil spring 93 having one end secured to the supporting sleeve 94 of disc 90 and having its other end secured to the opposite sidewall of housing 82, as shown in FIG. 4. Thus, the spring 93 engages around the sleeve 94 and biases the disc member 90 in a counterclockwise direction, as viewed in FIG. 4, whereby to urge the lug 91 into engagement with the stationary arm 92. The spring 93 thus biases the disc 90 toward its starting position.

Rotatably mounted on shaft 83 adjacent sleeve 94 is another sleeve 95 which is formed integrally with a disc member 96 projecting perpendicularly to shaft 83, as shown in FIG. 5. Mounted on the marginal portion of disc member 96 and extending parallel to sleeve 95 is a normally open limit switch 97 having an operating arm 98, the arm 98 being located so that its end portion projects in the path of rotation of lug 91. A horizontal adjusting screw 99 is rotatably journaled in the upper portions of the sidewalls of the housing 82, one end of screw 99 being provided with a manually-operated crank portion 100. Threadedly engaged on the screw 99 is a nut member 101 provided with a rearwardly projecting horizontal pin 102 which slidably engages in a radial slot 103 formed in the disc member 96, the nut member 101 being generally rectangular in cross section and having the rear edge thereof bearing against the disc 96 so that it is held against rotation relative thereto. Thus, when the screw 99 is rotated, the nut member 101 travels along the screw and the pin 102 camminglycooperates with the radial slot 103 to adjust the rotated position of the disc member 96. This adjusts the position of the limit switch 97 and correspondingly adjusts the angular distance required for the lug 91 to travel from its starting position to a position of engagement with the end of the operating arm 98. When lug 91 engages the end of the operating arm 98, switch 97 is operated so that its pole 104 moves into engagement with stationary contact 105. Thus, the closure of contacts 104,105 will occur after a predetermined amount of angular rotation of ground-engaging wheel 16, subsequent to the energization ofthe measuring device clutch coil 89, and in accordance with the adjusted position of disc 96. As will be presently explained, when the contacts 104,105 close, the mechanism is placed under the control of the photoelectric sensing unit 51, which, upon being triggered by the presence of a plant therebeneath, causes energization of the main drive clutch coil 35 and of the latch-releasing solenoid 66.

As will be presently described, the energization of the main driving clutch assembly 21 produces rotation of cam 58 and causes contacts 76,77 to open, which deenergizes the measuring device clutch coil 89. This allows the return spring 93 to return disc 90 to its starting position, namely, to a position wherein projection 91 abuts stop arm 92.

Mounted on the frame member 12 forwardly of the distance-measuring unit 81 is a housing 106 containing a suitable source of electrical power, such as a battery, or the like, and also containing additional elements of the electrical control circuit associated with the apparatus, such as a pair of relays 107 and 108 diagrammatically shown in FIG. 9, The source of current is employed to energize the light source 53 by circuit means, not shown, and is also used to energize the other circuit elements of the apparatus. Thus, a pair of line wires 109 and 110, shown in FIG. 9, are connected to the respective poles of the aforesaid current source.

The relay 107 has a winding 111 and has two poles 112 and 113. The pole 112 is engageable with a stationary contact 114 responsive to the energization of relay winding 111. The pole 113 normally engages a stationary contact 115, but is movable away from contact 115 into engagement with another stationary contact 116 responsive to the energization of winding As shown in FIG. 9, line wire 110 is connected through the 7 limit switch contacts 76,77 and a wire 122 to one terminal of the measuring device clutch coil 89. The other terminal of coil 89 is connected by a wire 123 to the relay contact 115. The relay pole 113 is connected by a wire 124 to the line wire 109. The pole 104 of limit switch 97 is likewise connected to wire 109. Switch contact 105 is connected by wire 125 to one terminal of relay winding 111. The remaining terminal of winding 111 is connected by a wire 126 to wire 122. Relay contact 116 is connected by a wire 127 to wire 125. Thus, in the starting position of the apparatus shown in FIG. 9, the measuringcause relay coil 11] to be energized through a circuit comprising line wire 109, contacts 104.105, wire 125, relay coil 111, wire 126, wire 122, contacts 76,77 and line wire 110, With coil 111 energized, pole 113 swings away from contact into engagement with contact 116 and pole 112 swings into engagement with contact 114. Thus, clutch coil 89 becomes deenergized by the opening ofcontacts 113,116, but relay coil 11'] is maintained energized by the closure of the contacts 113,116 which connects wire to wire 109 through wire 127, contacts 113,116, and wire 124,

The deenergization of coil 89 uncouples disc elements 87 and 90, allowing spring 93 to reset disc element 90 to its initial position, as above-described,,in preparation for the next measuring cycle.

Referring now to the relay 108, one terminal of its winding 117 is connected by wires 129 and 130 to line wire 109. The remaining terminal of winding 117 is connected by a wire 131 to relay pole 112. The associated stationary contact 114 is connected by a wire 132 to the photocell relay stationary contact 57. The photocell relay pole 56 is connected by a wire 133 to the limit switch stationary contact 78. The limit switch pole 75 is connected by a conductor 134 to wire 131. Wire 133 is connected by a wire 135 to line wire 110.

One terminal of the main drive clutch coil 35 is connected to the wire 130 and the other terminal thereof is connected to relay pole 118. Similarly, one terminal of latching solenoid 66 is connected to wire 130 and the other terminal thereof is connected through limit switch contacts 79,80 and a wire 136 to relay pole 119. The stationary contacts 120 and 121 associated with the relay poles 118 and 119 are connected to wire 135, as shown.

As above-mentioned, after a measured distance of travel from the startingposition, the relay winding 111 will be come energized by the closure of contacts 104,105 of limit switch 97. Winding 111 will be retained energized by the closure of contacts 116,115. Relay contacts 112,114 close and prepare an energizing circuit for relay winding 117 comprising line wire 109, wire 130, wire 129, relay winding 11.7, wire 131, contacts 112,114, wire 132, the normally open photocell relay contacts 56,57, wire 133, wire 135, and line wire 110. When the photocell 52 detects a plant, it triggers relay 55, closing contacts 56,57, and thereby energizing relay winding 117 by the above-described circuit. Relay contacts 118, 120 and 119,121 close, thereby energizing the main drive clutch coil 35 through a circuit comprising wire 109, wire 130, coil 35, contacts 118,120, wire 135, and line wire 110. Latching solenoid winding 66 is like wise energized through a circuit comprising line wire 109, wire 130, winding 66, limit switch contacts 79,80, wire 136, relay contacts 119,121, wire 135, and line wire 110.

The energization of clutch coil 35 drivingly couples disc element 24 to disc element 22 and drive shaft 18 in the manner above-described, the latching cam 58 being released because of the energization of solenoid 66, so that arm 62 is disengaged for from beneath the locking shoulder 60 which was in engagement with the top end of arm 62 at the starting position. This rotates shaft 40 in the manner above-described to begin one swing of the thinning blade members 48,48, for example, from the full-line position thereof shown in FIG. 6, toward the dotted-view position thereof. As shaft 18 begins its clockwise rotation, as viewed in FIG. 7, limit switch 73 is released to close its contacts 75,78 and to open its contacts 76,77, as above-described. The opening of contacts 76,77 deenergizes relay 107, but the relay winding 117 is maintained energized by the closure of contacts 75,76 through a circuit comprising line wire 109, wire 130, wire 129, winding 117, conductor 134, contacts 75,78, wire 135, and line wire 110. This maintains drive clutch coil 35 energized through the half revolution of rotation of cam disc 58 which accompanies one swing of the thinning blade members 48,48.

Shortly after limit switch 73 is released, the limit switch 74 is likewise released, as above-described, causing contacts 79,80 to open, whereby the latching solenoid winding 66 is deenergized. Spring 64 thus acts against arm 62 to rotate the arm toward locking position, namely, moves the arm 62 against the edge of cam segment 59 in a position to lockingly engage with the next locking shoulder 60 at the end of a half revolution of cam 58. At said end of the half revolution ofcam 58, abutment element 69 engages the roller on the end of operating arm 72 of limit switch 74 and abutment element 70 engages the roller on the end of the operating arm 71 of limit switch 73, restoring switches 74 and 73 to their starting conditions, shown in FIG. 9. Relay winding 117 becomes deenergized by the opening of contacts 75,78, so that main drive clutch coil 35 becomes deenergized by the opening of the relay contacts 118,120, and latching solenoid 66 cannot be reencrgized because of the opening of relay contacts 119,121. Thus, the parts are returned to their starting positions in preparation for the next cycle of operation, which begins with the closure of the contacts 76,77 and the energization of the measuring device clutch coil 89, as above-described.

it will thus be seen that the cycle of operation of the device comprises first, a movement of the machine through a measured distance with one of the blade elements 49 in cutting position, as shown in FIG. 6, severing undesired plants, until limit switch contacts 104,105 close, causing energization of relay 107, which places the apparatus under the control of the photoelectric unit 51, by the closure of relay contacts 112,114. When the photocell 52 responds to the presence of a plant there beneath relay 108 becomes energized by the closure of photo electric contacts 56,57, unlatching the cam 58 and energizing the main drive clutch coil 35, thereby causing the arms 48,48 to swing through one-half an oscillation, for example, from the full-line view position of FIG. 6, to the dotted-line view position, during the course of which the machine is moving forwardly and during the course of which a plant is allowed to remain unsevered because of the clearance provided therefor between the opposing ends of the downwardly and inwardly directed blade elements 49,49. At the end of their half oscillation, another of the blade elements 49 will be in cutting position. Thus, the supporting bar 43 is alternateiy rocked back and forth in a periodic, intermittent manner, so that the blade elements 49 alternately sever a number of undesired plants, while the desired plants are untouched and are uniformly spaced along the row.

The optical system contained in the unit 51 is suitably designed to cause the photocell 52 to respond to the presence of a plant in the space beneath the unit 51. Thus, the unit 51 may be provided with suitable lenses and filters to direct reflected light of the proper spectral composition to the photocell 52 to cause said photocell to respond in the intended manner. A wide variety of different optical systems may be employed. For example, the optical system may be similar to that employed in the U. S. Pats. 2,438,224 and 2,633,785 to L. A. Marihart.

As above-mentioned, detection of a plant beneath the photoelectric unit 51 results in the closure of the relay contacts 56,57, whereby the energizing circuit for the control relay 108 is closed responsive to the closure of relay contacts 112,114. This occurs after a measured amount of movement of the machine, as above-described, as required to close the contacts 104,105. Thus, after themeasured distance has been traveled, if the photocell 52 sees" a plant therebeneath, the swinging action of the thinning blades is initiated in the manner above-described, during the course of which a plant will escape cutting because of the clearance provided between the spaced opposing sharp ends of the-blade members 49,49. 1f the photocell 52 sees" no plants therebeneath, the contacts 56,57 fail to close and relay 108 cannot become energized. Under these conditions, the blade assembly will remain in its last fully-swung position, namely, either in the position shown in full-line view in FIG. 6, or the position shown in dotted-line view in said FIG.

The circuitry associated with the photocell 52, the amplifier 54 and the relay 55 may be either of the vacuum-tube type or of the solid state type. The photosensitive element 52 may likewise be either of the tube type or solid-state type, or alternatively, may be of the photosensitive resistance type, with the associated circuitry correspondingly arranged to respond to changes in resistance.

light from the ground, whereby to prevent false closure of the contacts 56,57 in the absence of a plant beneath the photoelectric unit 51. The optical system employed includes suitable filters to create a distinctive response (unbalance) when the system sees" a plant therebeneath.

Basically, the photoelectric detector 51 may consist of a suitable light-gathering device. such as a tube, provided with a device to divide the incident light, such as an inclined half-silvered mirror placed in the tube, some of the rays passing through the mirror and the other rays being reflected laterally therefrom toward respective light-sensitive cells. By the use of proper filters a specific color can be blocked from one cell, but not from the other. The cells will then react differently to the presence of this color in the incident light reaching the unit 51. This difference in reaction is converted into the triggering signal which ultimately causes the closure of the con tacts 56,57.

While certain specific embodiments of an improved row crop thinning attachment for use in thinning rows of plants to desired spacings have been disclosed in the foregoing description, it will be understood that various modifications within the spirit of the invention may occur to those skilled in the art. Therefore, it is intended that no limitations be placed on the invention except as defined by the scope of the appended claims.

lclaim:

l. A plant thinner comprising a frame adapted to be attached to a hauling vehicle, a ground-engaging wheel journaled to said frame, a cutter assembly pivoted to said frame to swing transversely thereof and having spaced opposing cutter blades separated by a sufficient distance to allow passage of a plant therebetween while the blades are swinging during forward movement of the frame, means including a magnetic clutch drivingly connecting said wheel to said cutter assembly, photosensitive switch means on the frame closing responsive to the presence of plants therebeneath, distance-measuring switch means, means to close said distance-measuring switch means responsive to the forward movement of the frame a predetermined distance along the ground, a source of current, circuit means including said photosensitive switch means and said distance-measuring switch means operatively connecting said source of current to said magnetic clutch, wherein the means drivingly connecting said wheel to said cutter assembly comprises a hollow shaft member journaled in the frame, means drivingly coupling the wheel to said hollow shaft member, a solid shaft member extending through said hollow shaft member, transmission means drivingly coupling said solid shaft member to said cutter assembly, said magnetic clutch being connected between said hollow shaft member and said solid shaft member, a latching cam on said solid shaft member, said cam having at least one locking shoulder, a locking arm movably mounted on the frame, means biasing said locking arm toward a locking position adjacent said locking shoulder to prevent rotation of the solid shaft member, electromagnetic release means connected through said locking arm to disengage said locking arm from said locking shoulder, and means to energize said release means responsive to the closure of both said photosensitive switch means and said distance-measuring switch means.

' 2'. The plant thinner of claim 1, and wherein said distancemeasuring switch means comprises a rotary shaft journaled on the frame, means to drive said last-named shaft responsive to movement of the frame along the ground, a normally deenergized relay n the frame having a pair of normally open switch contacts, a normally open limit switch mounted on the frame, an energizing circuit including said limit switch connected to said relay, an abutment shoulder rotatably mounted on said A suitable balanced arrangement of photosensitive elemerits may be employed to compensate for normal reflected last-named shaft and being operatively engageable with said limit switch at'a rotated position thereof, means biasing said abutment member toward a starting position spaced from said rotated position, and releasable coupling means drivingly connecting said last-named shaft to said abutment member.

3. The plant thinner of claim 2, and wherein said releasable coupling means comprises a magnetic clutch.

4. The plant thinner of claim 3, and wherein said relay has a pair of normally closed contacts, and circuit means connecting said source of current to said last-named magnetic clutch through said pair of normally closed relay contacts, whereby the last-named magnetic clutch becomes deenergized responsive to the energization of the relay to release the abutment member from said last-named shaft.

5. The plant thinner of claim 4, and a holding circuit connecting said relay to said source of current responsive to the energization of the relay; further limit switch means closing responsive to the rotation of the latching cam from its starting position, means connecting said first-named magnetic clutch to said source of current through said further limit switch means, means opening said relay-holding circuit as the cutter blades begin their swinging movement, and means opening said further limit switch means as the blades complete onehalfan oscillation thereof.

6. The plant thinner of claim 2, and wherein said limit switch is provided with a support rotatably mounted on said rotary shaft, whereby the limit switch is rotatably adjustable around the axis of rotation of the abutment member, a screw member rotatably mounted on the frame and extending substantially parallel to the last named support, and nut means on the screw memberdrivingly engaged with said last-named support to angularly adjust said last-named support responsive to rotation of the screw member, whereby to adjust the position of the limit switch relative to the starting position of the abutment member.

7. A plant thinner comprising a frame adapted to be attached to a hauling vehicle, a ground-engaging wheel journaled to said frame, a cutter assembly pivoted to said frame to swing transversely thereof and having spaced opposing cutter blades separated by a sufficient distance to allow passage of a plant therebetween while the blades are swinging during forward movement of the frame, means including a magnetic clutch drivingly connecting said wheel to said cutter assembly, photosensitive switch means on the frame closing responsive to the presence of plants therebeneath, distance-measuring switch means, means to close said distance-measuring switch means responsive to the foward movement of the frame a predetermined distance along the ground, a source of current, circuit means including said photosensitive switch means and said distance measuring switch means operatively connect ing said source of current to said magnetic clutch, and means drivingly connecting said wheel to said cutter assembly com prising a hollow shaft member journaled in the frame. means drivingly coupling the wheel to said hollow shaft member, a solid shaft member extending through said hollow shaft member, transmission means drivingly coupling said solid shaft member to said cutter assembly, and said magnetic clutch being connected between said hollow shaft member and said solid shaft member.

8. The plant thinner of claim 7, and wherein said transmission means comprises an inclined wobble disc secured on said solid shaft member, and a race ring rotatably mounted on the periphery of said wobble disc, said cutter assembly being provided with a supporting shaft journaled on the frame, a yoke member on said supporting shaft receiving said race ring, and means pivotally connecting the arms of said yoke member to opposite portions of said race ring. 

